Encased electrical apparatus



July 3, 1

P. H. HOUSER ENCASED ELECTRICAL APPARATUS 7 Filed July 19, 1950Irv/enter: Philip H.HOUS6T",

HIS Attorney.

United States Patent 2,753,533 ENCASED ELECTRICAL APPARATUS Philip H.Houser, Swampscott, Mass., assignor to General Electric Company, acorporation of New York Application July 19, 1950, Serial No. 174,761

2 Claims. (Cl. 336-96) My invention relates to encased electricalapparatus, and more particularly to static electric translatingapparatus of the type comprising an electric translating device embeddedin a fluid-impervious molded casing. My invention is particularlyadapted for use with directburial type transformers of the kind used asinsulating transformers in series lighting circuits, and the like.Direct burial of such transformers is particularly desirable in airportrunway lighting circuits, and the like, where no poles or subterraneanvaults are provided.

It has not been uncommon heretofore to encase electrical apparatus, andparticularly transformers, ignition coils, and the like, in variousinsulating compounds by positioning the electrical device in anopen-ended container and filling the container with an insulatingcomposition. Various materials, such as asphaltic compositions,artificial rubbers, and various synthetic resins and polymerizablesolventless varnishes have been used for this purpose. The ordinarypractice with such devices is to leave the lead wires protruding fromthe open end of the molded casing, so that the lead wires provide anattractive, if not a proper, handle for lifting and carrying thedevice'dur-ing shipping and installation. Such handling of the device bythe lead wires places an undue strain upon these Wires and upon theinsulating composition immediately adjacent the wires. It has been foundin the past, especially where a good bond is not formed between thewires and the immediately adjacent insulating composition that, as aresult of such handling, the insulating composition molded around thewires is frequently cracked away or otherwise separated therefrom at thepoint of entrance of the wires into the mass of insulating material.Such cracks frequently extend deep into the insulating composition andprovide paths for the entrance of moisture into the electrical deviceitself, thereby shortening life and frequently causing failure of thedevice in operation.

Accordingly, therefore, it is a general object of my invention toprovide a new and improved static electrical apparatus, embedded in afluid-impervious molded casing.

It is a further object of my invention to provide a new and improvedcable entrance support and seal for electric translating apparatusembedded in .a fluid-impervious molded insulating casing.

It is a still further object of my invention to provide a new andimproved direct'burial type encased electrical transformer, or the like,capable of being handled by its leads without adversely affecting themoistureproof and insulating qualities of the transformer.

In accordance with a preferred embodiment of my invention, I provideeach lead wire of a translating device to be encased in a cast body ofinsulating material with an annular resilient rubber gland, and I clampthe glands tightly against the wires and between a pair of aperturedclamping plates, at least one of which is formed as a precast block offluid-impervious electric insulating com- Patented July 3, 1956 pound.Having thus made a good mechanical seal around the lead wires by meansof the clamped resilient glands, I then cast the entire apparatus,including at least that surface of the precast insulating clamping platewhich is adjacent the translating device, into an integral cast ormoulded body of the same or a compatible, insulating material from whichthe clamping plate is preformed. This outer cast body of insulatingmaterial fills the interstices between the parts and forms a goodfluid-irnpervious bond with the precast clamping plate. I find that inthis manner a translating device and its lead wires may be effectivelysealed, even though the encasing compound would not itself form a goodbond with the wire insulation which may be of a different material.

My invention itself will be more fully understood and its variousobjects and advantages further appreciated by referring now to thefollowing detailed specification taken in conjunction With theaccompanying drawing, the single figure of which shows, partly insection, an encased electrical apparatus embodying my invention.

Referring now to the drawing, I have there shown a preferred embodimentof my invention wherein a transformer including a magnetizable frame I,a coil 2 and insulated lead wires or cables 3 is cast into an integralmolded body 4 of fluid-impervious insulating compound. The insulatingcompound from which the body 4 is molded may be any suitablethermoplastic or thermosetting insulating compound such as an asphalticcompound, a synthetic resin, solventless varnish, or the like. I preferto use for this purpose a polymerizable solventless varnish compoundwith a suitable filler such as talc or the like. The lead wires 3 areprovided With insulating casings, and the other insulation is preferablyformed of a fluid-impervious resilient material, such as natural orartificial rubber or the like. Specifically, I prefer to use for theexternal insulating coating of the wires 3 an artificial rubber, such asneoprene, chloroprene, thiokol, or the like.

I find that where such a transformer and its leads are embedded in amolded casing such as the body 4, a good fluid-tight bond is notordinarily formed between the molded body and the lead insulation,especially where a different insulating material is used for the moldedbody than on the leads.

For the purpose of sealing and supporting the lead Wires 3, I provideupon each lead Wire an annular rubber gland 5 compressed between a pairof clamping plates 6 and 7. The clamping plate 6 is formed as anL-shaped angle iron, or bar 6a fixedly mounted upon the transformerframe I and having its overhanging flange 6 apertured to provide passagetherethrough of the lead wires The clamping plate 7 is formed as aprecast apertured block of electric insulating compound, and is boltedto the clamping plate or flange 6 by means of a plurality of clampingbolts 8, only one of which is shown, the plates 6 and 7 compressingbetween them the resilient cable glands 5.

The precast clamping plate or block 7 is formed of the same compound ofwhich the casing 4 is formed and provided with apertures through whichthe lead wires 3 pass. These apertures are of a size to fit closely overthe wires 3, and are of a sufficient length, i. e., the plate 7 issufficiently thick, to provide appreciable mechanical support for thewires 3 and prevent distortion or displacement of the glands 5. The leadwire apertures in the insulating clamping plate 7 are reamed out andenlarged conically at the side adjacent the cooperating clamping plate6, thereby to ensure Wedging of the annular rubber glands tightlyagainst the sides of the lead wires. This clamping plate and glandstructure provides a tight, fluidimpervious mechanical seal between thelead wires and the annular rubber glands, and also firmly supports thelead wires immediately above the glands thereby to prevent displacementof the glands by distortion of the outer leads.

After the lead wires 3 are firmly clamped in the structure describedabove, the entire apparatus is embedded in the cast or molded body 4 ofelectric insulating compound. This compound fills the intersticesbetween the parts and forms an integral fluid-impervious outer casing.The encasing body 4 is formed of the same insulating compound as is theprecast clamping member or plate 7, and preferably completely embeds theentire transformer or other translating device as well as both clampingplates 6 and 7, as illustrated. It will of course be understood thatwithout departing from the spirit or scope of my invention the preformedclamping plate 7 and the outer cast body 4 may be formed of compoundswhich, though not of identical composition, are compatible or similar atleast to the extent that they form at their contacting surfaces a goodfluid-tight bond.

It will be further understood by those skilled in the art that it is notessential that the entire clamping plate 7 be embedded in the body 4,but it is only necessary that at least that face of the clamping plate 7on the side adjacent the encased translating apparatus be so embedded,whereby a fluid-tight seal is formed between the encasing body 4 and thegland receiving side of the precast insulating clamping plate 7.Moreover, it is not necessary that the clamping plate 6 be fixedlymounted upon the translating apparatus, nor that it be positioned onthat side of the insulating clamping plate 7 which is adjacent thetranslating apparatus. If the clamping plate 6 is positioned on theremote or outer side of the clamping plate 7, it is not essential to theformation of a good seal that the plate 6 be even partially embedded inthe insulating body 4. It is, of course, desirable that both clampingplates be embedded whatever their relative positions.

As previously indicated, the juncture between the precast clamping plate7 of insulating compound and the outer molded casing 4 of the sameinsulating compound forms a good fluid-impervious bond or seal. Thisbond, in conjunction with the mechanical seal between the compressedrubber glands and the lead wires 3, completely isolates the encasedtranslating apparatus from external moisture. In addition, the leadwires 3 are mechanically supported by the clamping plate 7, so that thedeformation of the external portions of the wires does not affect thesealing of the wires.

1 have further found that the bond between the precast clamping plate 7of insulating compound and the 'outer encasing body 4 of the sameinsulating compound is improved if the body 4 is cast before theclamping plate 7 is fully cured. For this purpose I prefer to inhibitcuring of the clamping plate 7, as by coating the mold from which theplate is formed, at least at those portions of the plate which willultimately contact the body 4, with a cure inhibiting compound. Suchcompound may, for example, be as an antioxidant which would retardpolymerization at the surface of the cast material. The encasing body 4,when it is cast, normally includes a curing agent, and this curing agentis sufficient to cure both the body 4 and complete the curing of theclamping plate 7. Such curing agent may, for example, comprise apolymerization catalyst, such as benzoyl peroxide, when using asolventless varnish compound.

While I have described only a preferred embodiment of my invention byway of illustration, many modifications will occur to those skilled inthe art, and I, therefore, wish to have it understood that I intend inthe appended claims to cover all such modifications as fall within thetrue spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric translating apparatus comprising a static electrictranslating device having electric conducting lead wires covered with afluid-impervious resilient electric insulating material, a resilientannular gland encircling each of said insulated wires, a pair ofclamping plates having aligned wire-receiving apertures positioned onopposite sides of said glands, the clamping plate remote from saidtranslating device being formed as a precast body of molded electricinsulating compound having an appreciable thickness and apertured to fitsnugly over said wires, means for drawing said plates together tocompress said glands and form a tight mechanical seal between saidglands and the associated wires, and an outer cast body formed of amolded insulating compound similar to that of said remote clampingplate, said outer body completely embedding said translating device theadjacent clamping plate and at least that side of said remote clampingplate adjacent said translating device, whereby said remote clampingplate supports said wires and seals said wires against said glands whilemaldng a fluid-tight bond with said outer cast body of insulatingmaterial.

2. An electromagnetic induction apparatus including a magnetizable frameand a winding thereon having insulated lead wires extending therefrom,said wires being covered with an external insulating coating ofresilient ruid-impervious electric insulating material, a bracket fixedto said frame and provided with an apertured overhanging flange throughwhich said lead wires extend, a resilient annular sealing glandencircling each said insulated wire adjacent said flange on the sidethereof remote from said frame and winding, an apertured clamping plateformed of precast electric insulating compound and disposed on saidwires to hold said glands in clamping relation against said wiresbetween said clamping plate and said apertured flange, said clampingplate being sufiiciently thick and the apertures therein fitting closelyover said wires thereby mechanically to support said wires, theapertures in said clamping plate being conically enlarged adjacent saidglands to wedge said glands against said wires, and an outer cast bodyof molded electric insulating compound completely embedding said frame,winding and bracket and at least that side of said clamping plateadjacent said bracket, said outer body being formed of the sameinsulating compound as said clamping plate and forming a fluid-tightbond therewith.

References Cited in the file of this patent UNITED STATES PATENTS1,763,115 Wermine June 10, 1930 1,851,940 Williams 1 Mar. 29, 19321,884,071 Menzel Oct. 25, 1932 2,343,725 Wilson Mar. 7, 1944 2,376,427Handforth et al. May 22, 1945 2,383,926 White Aug. 28, 1945 2,391,038Rifenbergh Dec. 18, 1945 FOREIGN PATENTS 611,526 Great Britain Nov. 1,1948 OTHER REFERENCES Abstract: Houser, 7,005, published in O. G. MarchReview of Scientific Instruments, vol. 15, No. 2, Feb. 1944, pages46-47. V

